Respiratory mask



FIG. 1 is a front perspective view of a portion of a frame for a respiratory mask according to an embodiment of our design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof; and,

FIG. 4 is a left view thereof, with the right side view thereof being a mirror image thereof.

Where included, phantom lines represent environment or structure and do not form part of the claimed design.

Where included, dotted lines represent the border between claimed and non-claimed subject matter and form no part of the claimed design. 

The ornamental design for a respiratory mask, as shown and described. 